Search for a Two-Higgs-Boson Doublet Using a Simplified
Model in pp[over ¯] Collisions at sqrt[s]=1.96TeV
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Citation
Aaltonen, T., J. Adelman, B. Álvarez González, S. Amerio, D.
Amidei, A. Anastassov, A. Annovi, et al. Search for a TwoHiggs-Boson Doublet Using a Simplified Model in Pp[over ¯]
Collisions at sqrt[s]=1.96TeV. Physical Review Letters 110, no.
12 (March 2013).
As Published
http://dx.doi.org/10.1103/PhysRevLett.110.121801
Publisher
American Physical Society
Version
Final published version
Accessed
Thu May 26 06:46:22 EDT 2016
Citable Link
http://hdl.handle.net/1721.1/82132
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Detailed Terms
PRL 110, 121801 (2013)
week ending
22 MARCH 2013
PHYSICAL REVIEW LETTERS
Search for a Two-Higgs-Boson Doublet
pffiffiffi Using a Simplified Model
in pp Collisions at s ¼ 1:96 TeV
T. Aaltonen,22 J. Adelman,58 B. Álvarez González,10,aa S. Amerio,41a D. Amidei,33 A. Anastassov,16,y A. Annovi,18
J. Antos,13 G. Apollinari,16 J. A. Appel,16 T. Arisawa,55 A. Artikov,14 J. Asaadi,50 W. Ashmanskas,16 B. Auerbach,58
A. Aurisano,50 F. Azfar,40 W. Badgett,16 T. Bae,26 A. Barbaro-Galtieri,27 V. E. Barnes,45 B. A. Barnett,24 P. Barria,43c,43a
P. Bartos,13 M. Bauce,41b,41a F. Bedeschi,43a S. Behari,24 G. Bellettini,43b,43a J. Bellinger,57 D. Benjamin,15 A. Beretvas,16
A. Bhatti,47 D. Bisello,41b,41a I. Bizjak,29 K. R. Bland,5 B. Blumenfeld,24 A. Bocci,15 A. Bodek,46 D. Bortoletto,45
J. Boudreau,44 A. Boveia,12 L. Brigliadori,6b,6a C. Bromberg,34 E. Brucken,22 J. Budagov,14 H. S. Budd,46 K. Burkett,16
G. Busetto,41b,41a P. Bussey,20 A. Buzatu,32 A. Calamba,11 C. Calancha,30 S. Camarda,4 M. Campanelli,29 M. Campbell,33
F. Canelli,12,16 B. Carls,23 D. Carlsmith,57 R. Carosi,43a S. Carrillo,17,n S. Carron,16 B. Casal,10,l M. Casarsa,51a
A. Castro,6b,6a P. Catastini,21 D. Cauz,51a V. Cavaliere,23 M. Cavalli-Sforza,4 A. Cerri,27,g L. Cerrito,29,t Y. C. Chen,1
M. Chertok,7 G. Chiarelli,43a G. Chlachidze,16 F. Chlebana,16 K. Cho,26 D. Chokheli,14 W. H. Chung,57 Y. S. Chung,46
M. A. Ciocci,43c,43a A. Clark,19 C. Clarke,56 G. Compostella,41b,41a M. E. Convery,16 J. Conway,7 M. Corbo,16
M. Cordelli,18 C. A. Cox,7 D. J. Cox,7 F. Crescioli,43b,43a J. Cuevas,10,aa R. Culbertson,16 D. Dagenhart,16 N. d’Ascenzo,16,x
M. Datta,16 P. de Barbaro,46 M. Dell’Orso,43b,43a L. Demortier,47 M. Deninno,6a F. Devoto,22 M. d’Errico,41b,41a
A. Di Canto,43b,43a B. Di Ruzza,16 J. R. Dittmann,5 M. D’Onofrio,28 S. Donati,43b,43a P. Dong,16 M. Dorigo,51a T. Dorigo,41a
K. Ebina,55 A. Elagin,50 A. Eppig,33 R. Erbacher,7 S. Errede,23 N. Ershaidat,16,ee R. Eusebi,50 S. Farrington,40 M. Feindt,25
J. P. Fernandez,30 R. Field,17 G. Flanagan,16,v R. Forrest,7 M. J. Frank,5 M. Franklin,21 J. C. Freeman,16 Y. Funakoshi,55
I. Furic,17 M. Gallinaro,47 J. E. Garcia,19 A. F. Garfinkel,45 P. Garosi,43c,43a H. Gerberich,23 E. Gerchtein,16 S. Giagu,48a
V. Giakoumopoulou,3 P. Giannetti,43a K. Gibson,44 C. M. Ginsburg,16 N. Giokaris,3 P. Giromini,18 G. Giurgiu,24
V. Glagolev,14 D. Glenzinski,16 M. Gold,36 D. Goldin,50 N. Goldschmidt,17 A. Golossanov,16 G. Gomez,10
G. Gomez-Ceballos,31 M. Goncharov,31 O. González,30 I. Gorelov,36 A. T. Goshaw,15 K. Goulianos,47 S. Grinstein,4
C. Grosso-Pilcher,12 R. C. Group,53,16 J. Guimaraes da Costa,21 S. R. Hahn,16 E. Halkiadakis,49 A. Hamaguchi,39
J. Y. Han,46 F. Happacher,18 K. Hara,52 D. Hare,49 M. Hare,53 R. F. Harr,56 K. Hatakeyama,5 C. Hays,40 M. Heck,25
J. Heinrich,42 M. Herndon,57 S. Hewamanage,5 A. Hocker,16 W. Hopkins,16,h D. Horn,25 S. Hou,1 R. E. Hughes,37
M. Hurwitz,12 U. Husemann,58 N. Hussain,32 M. Hussein,34 J. Huston,34 G. Introzzi,43a M. Iori,48b,48a A. Ivanov,7,q
E. James,16 D. Jang,11 B. Jayatilaka,15 E. J. Jeon,26 S. Jindariani,16 A. Johnstone,8 M. Jones,45 K. K. Joo,26 S. Y. Jun,11
T. R. Junk,16 T. Kamon,23,50 P. E. Karchin,56 A. Kasmi,5 Y. Kato,39,p W. Ketchum,12 J. Keung,42 V. Khotilovich,50
B. Kilminster,16 D. H. Kim,26 H. S. Kim,26 J. E. Kim,26 M. J. Kim,18 S. B. Kim,26 S. H. Kim,52 Y. K. Kim,12 Y. J. Kim,26
N. Kimura,55 M. Kirby,16 S. Klimenko,17 K. Knoepfel,16 K. Kondo,55,a D. J. Kong,26 J. Konigsberg,17 A. V. Kotwal,15
M. Kreps,25 J. Kroll,42 D. Krop,12 M. Kruse,15 V. Krutelyov,50,d T. Kuhr,25 M. Kurata,52 S. Kwang,12 A. T. Laasanen,45
S. Lami,43a S. Lammel,16 M. Lancaster,29 R. L. Lander,7 K. Lannon,37,z A. Lath,49 G. Latino,43c,43a T. LeCompte,2
E. Lee,50 H. S. Lee,12,r J. S. Lee,26 S. W. Lee,50,cc S. Leo,43b,43a S. Leone,43a J. D. Lewis,16 A. Limosani,15,u C.-J. Lin,27
M. Lindgren,16 E. Lipeles,42 A. Lister,19 D. O. Litvintsev,16 C. Liu,44 H. Liu,54 Q. Liu,45 T. Liu,16 S. Lockwitz,58
A. Loginov,58 D. Lucchesi,41b,41a J. Lueck,25 P. Lujan,27 P. Lukens,16 G. Lungu,47 J. Lys,27 R. Lysak,13,f R. Madrak,16
K. Maeshima,16 P. Maestro,43c,43a S. Malik,47 G. Manca,28,b A. Manousakis-Katsikakis,3 F. Margaroli,48a C. Marino,25
M. Martı́nez,4 P. Mastrandrea,48a K. Matera,23 M. E. Mattson,56 A. Mazzacane,16 P. Mazzanti,6a K. S. McFarland,46
P. McIntyre,50 R. McNulty,28,k A. Mehta,28 P. Mehtala,22 C. Mesropian,47 T. Miao,16 D. Mietlicki,33 A. Mitra,1
H. Miyake,52 S. Moed,16 N. Moggi,6a M. N. Mondragon,16,n C. S. Moon,26 R. Moore,16 M. J. Morello,43d,43a J. Morlock,25
P. Movilla Fernandez,16 A. Mukherjee,16 Th. Muller,25 P. Murat,16 M. Mussini,6b,6a J. Nachtman,16,o Y. Nagai,52
J. Naganoma,55 I. Nakano,38 A. Napier,53 J. Nett,50 C. Neu,54 M. S. Neubauer,23 J. Nielsen,27,e L. Nodulman,2 S. Y. Noh,26
O. Norniella,23 L. Oakes,40 S. H. Oh,15 Y. D. Oh,26 I. Oksuzian,54 T. Okusawa,39 R. Orava,22 L. Ortolan,4
S. Pagan Griso,41b,41a C. Pagliarone,51a E. Palencia,10,g V. Papadimitriou,16 A. A. Paramonov,2 J. Patrick,16
G. Pauletta,51b,51a M. Paulini,11 C. Paus,31 D. E. Pellett,7 A. Penzo,51a T. J. Phillips,15 G. Piacentino,43a E. Pianori,42
J. Pilot,37 K. Pitts,23 C. Plager,9 L. Pondrom,57 S. Poprocki,16,h K. Potamianos,45 F. Prokoshin,14,dd A. Pranko,27
F. Ptohos,18,i G. Punzi,43b,43a A. Rahaman,44 V. Ramakrishnan,57 N. Ranjan,45 K. Rao,8 I. Redondo,30 P. Renton,40
M. Rescigno,48a T. Riddick,29 F. Rimondi,6b,6a L. Ristori,42,16 A. Robson,20 T. Rodrigo,10 T. Rodriguez,42 E. Rogers,23
S. Rolli,53,j R. Roser,16 F. Ruffini,43c,43a A. Ruiz,10 J. Russ,11 V. Rusu,16 A. Safonov,50 W. K. Sakumoto,46 Y. Sakurai,55
L. Santi,51b,51a K. Sato,52 V. Saveliev,16,x A. Savoy-Navarro,16,bb P. Schlabach,16 A. Schmidt,25 E. E. Schmidt,16
0031-9007=13=110(12)=121801(8)
121801-1
Ó 2013 American Physical Society
PRL 110, 121801 (2013)
PHYSICAL REVIEW LETTERS
week ending
22 MARCH 2013
T. Schwarz,16 L. Scodellaro,10 A. Scribano,43c,43a F. Scuri,43a S. Seidel,36 Y. Seiya,39 A. Semenov,14 F. Sforza,43c,43a
S. Z. Shalhout,7 T. Shears,28 P. F. Shepard,44 M. Shimojima,52,w M. Shochet,12 I. Shreyber-Tecker,35 A. Simonenko,14
P. Sinervo,32 K. Sliwa,53 J. R. Smith,7 F. D. Snider,16 A. Soha,16 V. Sorin,4 H. Song,44 P. Squillacioti,43c,43a M. Stancari,16
R. St. Denis,20 B. Stelzer,32 O. Stelzer-Chilton,32 D. Stentz,16,z J. Strologas,36 G. L. Strycker,33 Y. Sudo,52 A. Sukhanov,16
I. Suslov,14 K. Takemasa,52 Y. Takeuchi,52 J. Tang,12 M. Tecchio,33 P. K. Teng,1 J. Thom,16,h J. Thome,11
G. A. Thompson,23 E. Thomson,42 D. Toback,50 S. Tokar,13 K. Tollefson,34 T. Tomura,52 D. Tonelli,16 S. Torre,18
D. Torretta,16 P. Totaro,41a M. Trovato,43d,43a A. Truong,8 F. Ukegawa,52 S. Uozumi,26 A. Varganov,33 F. Vázquez,17,n
G. Velev,16 C. Vellidis,16 M. Vidal,45 I. Vila,10 R. Vilar,10 J. Vizán,10 M. Vogel,36 G. Volpi,18 P. Wagner,42 R. L. Wagner,16
T. Wakisaka,39 R. Wallny,9 S. M. Wang,1 A. Warburton,32 D. Waters,29 W. C. Wester III,16 D. Whiteson,42,c
A. B. Wicklund,2 E. Wicklund,16 S. Wilbur,12 F. Wick,25 H. H. Williams,42 J. S. Wilson,37 P. Wilson,16 B. L. Winer,37
P. Wittich,16,h S. Wolbers,16 H. Wolfe,37 T. Wright,33 X. Wu,19 Z. Wu,5 K. Yamamoto,39 D. Yamato,39 T. Yang,16
U. K. Yang,12,s Y. C. Yang,26 W.-M. Yao,27 G. P. Yeh,16 K. Yi,16,o J. Yoh,16 K. Yorita,55 T. Yoshida,39,m G. B. Yu,15 I. Yu,26
S. S. Yu,16 J. C. Yun,16 A. Zanetti,51a Y. Zeng,15 C. Zhou,15 and S. Zucchelli6b,6a
(CDF Collaboration)
1
Institute of Physics, Academia Sinica, Taipei, Taiwan 11529, Republic of China
2
Argonne National Laboratory, Argonne, Illinois 60439, USA
3
University of Athens, 157 71 Athens, Greece
4
Institut de Fisica d’Altes Energies, ICREA, Universitat Autonoma de Barcelona, E-08193, Bellaterra (Barcelona), Spain
5
Baylor University, Waco, Texas 76798, USA
6a
Istituto Nazionale di Fisica Nucleare Bologna, I-40127 Bologna, Italy
6b
University of Bologna, I-40127 Bologna, Italy
7
University of California Davis, Davis, California 95616, USA
8
University of California Irvine, Irvine, California 92697, USA
9
University of California Los Angeles, Los Angeles, California 90024, USA
10
Instituto de Fisica de Cantabria, CSIC-University of Cantabria, 39005 Santander, Spain
11
Carnegie Mellon University, Pittsburgh, Pennsylvania 15213, USA
12
Enrico Fermi Institute, University of Chicago, Chicago, Illinois 60637, USA
13
Comenius University, 842 48 Bratislava, Slovakia and Institute of Experimental Physics, 040 01 Kosice, Slovakia
14
Joint Institute for Nuclear Research, RU-141980 Dubna, Russia
15
Duke University, Durham, North Carolina 27708, USA
16
Fermi National Accelerator Laboratory, Batavia, Illinois 60510, USA
17
University of Florida, Gainesville, Florida 32611, USA
18
Laboratori Nazionali di Frascati, Istituto Nazionale di Fisica Nucleare, I-00044 Frascati, Italy
19
University of Geneva, CH-1211 Geneva 4, Switzerland
20
Glasgow University, Glasgow G12 8QQ, United Kingdom
21
Harvard University, Cambridge, Massachusetts 02138, USA
22
Division of High Energy Physics, Department of Physics, University of Helsinki and Helsinki Institute of Physics,
FIN-00014, Helsinki, Finland
23
University of Illinois, Urbana, Illinois 61801, USA
24
The Johns Hopkins University, Baltimore, Maryland 21218, USA
25
Institut für Experimentelle Kernphysik, Karlsruhe Institute of Technology, D-76131 Karlsruhe, Germany
26
Center for High Energy Physics, Kyungpook National University, Daegu 702-701, Korea; Seoul National University, Seoul 151-742,
Korea; Sungkyunkwan University, Suwon 440-746, Korea; Korea Institute of Science and Technology Information,
Daejeon 305-806, Korea; Chonnam National University, Gwangju 500-757,
Korea; and Chonbuk National University, Jeonju 561-756, Korea
27
Ernest Orlando Lawrence Berkeley National Laboratory, Berkeley, California 94720, USA
28
University of Liverpool, Liverpool L69 7ZE, United Kingdom
29
University College London, London WC1E 6BT, United Kingdom
30
Centro de Investigaciones Energeticas Medioambientales y Tecnologicas, E-28040 Madrid, Spain
31
Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, USA
32
Institute of Particle Physics: McGill University, Montréal, Québec H3A 2T8, Canada; Simon Fraser University,
Burnaby, British Columbia V5A 1S6, Canada; University of Toronto, Toronto, Ontario M5S 1A7,
Canada; and TRIUMF, Vancouver, British Columbia V6T 2A3, Canada
33
University of Michigan, Ann Arbor, Michigan 48109, USA
34
Michigan State University, East Lansing, Michigan 48824, USA
35
Institution for Theoretical and Experimental Physics, ITEP, Moscow 117259, Russia
121801-2
PHYSICAL REVIEW LETTERS
PRL 110, 121801 (2013)
week ending
22 MARCH 2013
36
University of New Mexico, Albuquerque, New Mexico 87131, USA
37
The Ohio State University, Columbus, Ohio 43210, USA
38
Okayama University, Okayama 700-8530, Japan
39
Osaka City University, Osaka 588, Japan
40
University of Oxford, Oxford OX1 3RH, United Kingdom
41a
Istituto Nazionale di Fisica Nucleare, Sezione di Padova-Trento, I-35131 Padova, Italy
41b
University of Padova, I-35131 Padova, Italy
42
University of Pennsylvania, Philadelphia, Pennsylvania 19104, USA
43a
Istituto Nazionale di Fisica Nucleare Pisa, I-56127 Pisa, Italy
43b
University of Pisa, I-56127 Pisa, Italy
43c
University of Siena, I-56127 Pisa, Italy
43d
Scuola Normale Superiore, I-56127 Pisa, Italy
44
University of Pittsburgh, Pittsburgh, Pennsylvania 15260, USA
45
Purdue University, West Lafayette, Indiana 47907, USA
46
University of Rochester, Rochester, New York 14627, USA
47
The Rockefeller University, New York, New York 10065, USA
48a
Istituto Nazionale di Fisica Nucleare, Sezione di Roma 1, I-00185 Roma, Italy
48b
Sapienza Università di Roma, I-00185 Roma, Italy
49
Rutgers University, Piscataway, New Jersey 08855, USA
50
Texas A&M University, College Station, Texas 77843, USA
51a
Istituto Nazionale di Fisica Nucleare Trieste/Udine, I-34100 Trieste, Italy
51b
University of Udine, I-33100 Udine, Italy
52
University of Tsukuba, Tsukuba, Ibaraki 305, Japan
53
Tufts University, Medford, Massachusetts 02155, USA
54
University of Virginia, Charlottesville, Virginia 22906, USA
55
Waseda University, Tokyo 169, Japan
56
Wayne State University, Detroit, Michigan 48201, USA
57
University of Wisconsin, Madison, Wisconsin 53706, USA
58
Yale University, New Haven, Connecticut 06520, USA
(Received 16 December 2012; published 18 March 2013)
We present a search for new particles in an extension to the standard model that includes a heavy Higgs
boson (H0 ), a lighter charged Higgs boson (H ), and an even lighter Higgs boson h0 , with decays leading
to a W-boson pair and a bottom-antibottom quark pair in the final state. We use events with exactly one
lepton, missing transverse momentum, and at least four jets in data corresponding to an integrated
pffiffiffi
luminosity of 8:7 fb1 collected by the CDF II detector in proton-antiproton collisions at s ¼ 1:96 TeV.
We find the data to be consistent with standard model predictions and report the results in terms of a
simplified Higgs-cascade-decay model, setting 95% confidence level upper limits on the product of
cross section and branching fraction from 1.3 pb to 15 fb as a function of H 0 and H masses for
m0h ¼ 126 GeV=c2 .
DOI: 10.1103/PhysRevLett.110.121801
PACS numbers: 12.60.Fr, 13.85.Rm, 14.80.Ec, 14.80.Fd
The study of the mechanism of electroweak-symmetry
breaking is one of the major thrusts of the experimental
high-energy-physics program. Following the discovery of
a Higgs-like boson at ATLAS [1] and CMS [2] with a
mass of approximately 126 GeV=c2 and complementary
evidence from CDF and D0 [3], the most pressing
question is whether this state is in fact the Higgs boson
of the standard model (SM), part of an extended Higgs
sector (such as that of the minimal supersymmetric
standard model [4]), a composite Higgs boson [5], or a
completely different particle with Higgs-like couplings
(such as a radion in warped extra dimensions [6] or a
dilaton [7]).
We search for particles in an extension to the standard
model that includes a light neutral Higgs boson h0 ,
with mass mh0 ¼ 126 GeV=c2 . Rather than assuming a
particular theoretical framework (such as the minimal
supersymmetric standard model), we follow a phenomenological approach, using a general two-Higgs-doublet
model as a convenient simplified model [8], which contains a heavy charged Higgs boson H and a heavier
neutral state H 0 . In this approach, the search for a number
of specific final states that have the strongest couplings to
Higgs particles is motivated [9,10]. The final state of a
W-boson pair (WW) is enhanced by WW scattering in
models where the Higgs sector is strongly coupled [11].
This signal has been the subject of much detailed investigation [12]. The phenomenology of resonant production
of the final states Zh0 [13] and W þ W Z [14] has also
been investigated.
121801-3
CDF Run II
Fraction of Events / 15 GeV/c 2
0.2
mH0 = 400 GeV/c22
mH± = 300 GeV/c
mH0 = 500 GeV/c2
mH± = 400 GeV/c2
mH0 = 600 GeV/c22
mH± = 400 GeV/c
0.18
0.16
0.14
0.12
0.1
0.08
0.06
0.04
0.02
0
0
50
100
150
200
250
H → WH± → WWh → WWbb
0
0
300
mbb [GeV/c2]
Fraction of Events / 35 GeV/c 2
CDF Run II
0.22
mH0 = 400 GeV/c22
mH± = 300 GeV/c
mH0 = 500 GeV/c2
mH± = 400 GeV/c2
mH0 = 600 GeV/c22
mH± = 400 GeV/c
0.2
0.18
0.16
0.14
0.12
0.1
0.08
0.06
0.04
0.02
0
100
200
300
400
500
H → WH± → WWh → WWbb
0
0
600
700
800
mWbb [GeV/c2]
Fraction of Events / 40 GeV/c 2
CDF Run II
mH0 = 400 GeV/c22
mH± = 300 GeV/c
mH0 = 500 GeV/c22
mH± = 400 GeV/c
mH0 = 600 GeV/c22
mH± = 400 GeV/c
0.25
0.2
0.15
0.1
0.05
0
200
300
400
500
600
H → WH± → WWh → WWbb
0
0
week ending
22 MARCH 2013
PHYSICAL REVIEW LETTERS
PRL 110, 121801 (2013)
700
800
900
1000
mWWbb [GeV/c2]
FIG. 1 (color online). Distribution of reconstructed Higgsboson masses in simulated events. Top, mh0 ¼ 126 GeV=c2
reconstructed as mbb ; center, mH as mWbb ; and bottom, mH0
as mWWbb .
In this Letter, we focus on the final state W þ W bb [15],
which can have a large production rate from the process
gg ! H 0 followed by H0 ! H W with H ! W h0 !
The W þ W bb final state is also the final state of
W bb.
top-quark pair production and has been extensively
studied. However, no search for Higgs-boson cascades as
described here has been reported previously, although
searches have been performed for charged Higgs bosons
in top-quark decays t ! H b [16–18].
We analyze a data sample corresponding to an integrated luminosity of 8:7 0:5 fb1 recorded by the CDF II
detector [19], a general
purpose detector designed to study
pffiffiffi
pp collisions at s ¼ 1:96 TeV in the Fermilab Tevatron
collider. The CDF tracking system consists of a silicon
microstrip tracker and a drift chamber that are immersed
in a 1.4 T axial magnetic field [20]. Projective-towergeometry electromagnetic and hadronic calorimeters surrounding the tracking system measure particle energies,
with muon detection provided by additional drift chambers
located outside the calorimeters.
The signature of H 0 ! W H ! W W þ h0 !
þ W W bb is a charged lepton (e or ), missing transverse
momentum, two jets arising from b quarks, and two additional jets from a W-boson hadronic decay. Events are
selected online (triggered) by the requirement of an electron
(e) or muon () candidate [21] with transverse momentum
pT [22] greater than 18 GeV=c. After trigger selection,
events are retained if the electron or muon candidate has a
pseudorapidity jj < 1:1 [22], with pT > 20 GeV=c, and
satisfies the standard CDF identification and isolation
requirements [21]. We reconstruct jets in the calorimeter
using the JETCLU [23] algorithm with a clustering radius of
0.4 in - space. The jets are calibrated using the techniques outlined in Ref. [24]. At least four jets are required,
each with transverse energy ET > 15 GeV and jj < 2:4.
Missing transverse momentum [25] is reconstructed using
calorimeter and muon information [21]; in the W þ W bb
experimental signature, the missing transverse momentum
is mostly due to the neutrino from the leptonically decaying
W boson. We require E
6 T > 20 GeV=c. Since such a signal
would yield two jets originating from b quarks, we require
(with minimal loss of efficiency) evidence of decay of a b
hadron in at least one jet. This requirement, called b tagging,
makes use of the SECVTX algorithm, which identifies jets
from b quarks via their secondary vertices [26].
We model the production of H 0 bosons with mH0 ¼
325–1100 GeV=c2 and subsequent decays H 0 ! W H with mH ¼ 225–600 GeV=c2 and decays H ! W h0
TABLE I. Contributions to the systematic uncertainty on the expected numbers of events for the two main background processes, the
total background yield, and an example 500 GeV=c2 Higgs-boson signal with an assumed total cross section of 1 pb.
Process
Predicted yield
Jet energy scale
Radiation
Q2 scale
Multiple interactions
tt generator
Normalization
Total systematic uncertainty
tt
W boson þ jets
Total background
Higgs boson
229
23%
3%
1%
5%
10%
26%
43
18%
6%
30%
35%
294
17%
2%
3%
2%
4%
16%
24%
341
12%
8%
15%
121801-4
bbww < 450 GeV/c2: > 1 lepton, > 4 jets, > 1 b tag CDF RunII
±
0
±
∫ L = 8.7 fb
mbbW > 200 GeV/c2 mbbWW > 450 GeV/c2
-1
- 0
+
+
H → W H → W W h → W W bb
data
tt
Multijets
W boson + jets
Others
120
100
80
60
40
20
20
40
60
80
100
120
140
160
180
0
200
50
100
150
200
bb mass [GeV/c2]
250
300
50
100
150
200
bb mass [GeV/c2]
250
300
bb mass [GeV/c ]
1
0.8
0.6
0.4
0.2
0
-0.2
-0.4
-0.6
-0.8
(Data-SM)/SM
(Data-SM)/SM
-1
Signal [250 fb]
data
tt
Multijets
W boson + jets
Others
2
20
40
60
80
100
120
140
160
180
1
0.8
0.6
0.4
0.2
0
-0.2
-0.4
-0.6
-0.8
200
bb mass [GeV/c2]
bbw < 250 GeV/c2: > 1 lepton, > 4 jets, > 1 b tag CDF RunII
120
Events/6.8 [GeV/c2]
∫ L = 8.7 fb
CDF RunII
140
-
Events/17 GeV/c2
Events/9.8 [GeV/c2]
200
180
160
140
120
100
80
60
40
20
0
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PHYSICAL REVIEW LETTERS
PRL 110, 121801 (2013)
±
±
+
- 0
∫ L = 8.7 fb
+
-1
FIG. 3 (color online). Distribution of events versus reconstructed bb invariant mass (mbb ) for observed data and expected
backgrounds in the signal region. A signal hypothesis is shown,
assuming a total cross section of 250 fb, mH0 ¼ 500 GeV=c2 ,
and mH ¼ 300 GeV=c2 . See Fig. 2 for descriptions of the lower
panel and hatching.
-
H → W H → W W h → W W bb
0
100
80
60
40
20
20
40
60
80
100
120
140
120
140
(Data-SM)/SM
bb mass [GeV/c2]
1
0.8
0.6
0.4
0.2
0
-0.2
-0.4
-0.6
-0.8
20
40
60
80
100
bb mass [GeV/c2]
FIG. 2 (color online). Distribution of events versus reconstructed bb invariant mass (mbb ) for observed data and expected
backgrounds in two control regions. Top: control region consisting of events with at least four jets, exactly zero b tags, and
mWWbb < 450 GeV=c2 . Bottom: control region consisting of
events with at least four jets and mWbb < 250 GeV=c2 . The
lower panels give the relative difference between the observed
and expected distributions; the hatched areas show the combined
statistical and systematic uncertainties of the expected background. The small dip near 80 GeV=c2 is mainly due to the
W-boson mass reconstruction.
The second largest SM background process is the
associated production of a W boson and jets. Samples of
W-boson þ jets events with light- and heavy-flavor (b, c)
quark jets are generated using ALPGEN [33] and interfaced
with a parton-shower model from PYTHIA. The W boson þ jets samples are normalized to the measured
W-boson-production cross section, with an additional multiplicative factor for the relative contribution of heavy- and
light-flavor jets, following Ref. [26].
Backgrounds due to production of a Z boson with additional jets, where the second lepton from the Z-boson decay
is not reconstructed, are small compared to the W-boson
background and are modeled using events generated with
ALPGEN interfaced to the parton-shower model from
PYTHIA. The multijet background, in which a jet is misreconstructed as a lepton, is modeled using events triggered
on jets and normalized to a background-dominated region at
600
1.2
550
1
2
H [GeV/c ]
500
0.8
450
0.6
400
±
with mh0 ¼ 126 GeV=c2 , all with MADGRAPH [27].
Additional radiation, hadronization, and showering are
described by PYTHIA [28]. The detector response for all
simulated samples is modeled by the GEANT-based CDF II
detector simulation [29].
The dominant SM background to this signature is topquark pair production. We model this background using
PYTHIA with a top-quark mass mt ¼ 172:5 GeV=c2 [30].
We normalize the tt background to the theoretical calculation at next-to-next-to-leading order in the strong interaction coupling constant s [31]. In addition, events
generated by a next-to-leading-order program MC@NLO
[32] are used in estimating an uncertainty in modeling
the radiation of an additional jet.
H0 → WH± → WWh0 → WWbb
350
0.4
300
CDF Run II
∫ L = 8.7 fb
250
400
500
600
700
800
900
0.2
-1
1000 1100
0
Observed Cross Section Limits [pb]
0
H0 [GeV/c2]
FIG. 4 (color online). Upper limits at 95% C.L. on the cross
section times branching fraction as a function of the Higgs-boson
masses mH and mH0 ; mh0 is fixed to 126 GeV=c2 in each case.
The diamonds show the grid of probed masses; the intermediate
values are interpolated.
121801-5
PRL 110, 121801 (2013)
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PHYSICAL REVIEW LETTERS
low missing transverse momentum where the multijet background is large.
The SM backgrounds due to production of single top
quarks and pairs of vector bosons are modeled using
MADGRAPH interfaced with PYTHIA parton-shower models
and PYTHIA, respectively, and normalized to next-toleading-order cross sections [34,35].
The Higgs-boson candidate mass reconstruction begins
with identification of the leptonically decaying W boson,
assuming the missing transverse momentum is due to the
resulting neutrino. Of the multiple solutions for the neutrino pseudorapidity, we use the smallest value that yields
the reconstructed W mass closest to the known value. The
hadronically decaying W boson is identified as the pair of
jets that yields the reconstructed dijet mass closest to the
known W mass, excluding jets with a b tag. If fewer than
two jets without b tags are present, the same procedure is
used but modified to include the b-tagged jets. The light h0
is reconstructed from the remaining b-tagged jets. If fewer
than two b-tagged jets remain, the jet or jets with largest
transverse momentum not associated with the hadronic
W-boson decay are used instead, without significant loss
of mass resolution. Figure 1 shows distributions of the
reconstructed mass for several choices of Higgs masses.
We enhance the signal-to-background ratio through
requirements on the mass of the W þ W bb and W bb
systems and search for an excess of events above expectations from backgrounds in event distributions versus the
Backgrounds have
mass of the bb system (h0 ! bb).
broad, smoothly decreasing distributions, while a signal
would be reconstructed near the Higgs-boson mass.
We consider several sources of systematic uncertainty
on the predicted background rates and distributions, as well
as on the expectations for a signal. Each systematic
uncertainty affects the expected sensitivity to a signal,
expressed as an expected cross section upper limit in the
no-signal assumption. The dominant systematic uncertainty is the jet-energy-scale uncertainty [24], followed
by theoretical uncertainties on the cross sections of the
background processes. To probe the description of additional jets, we compare our nominal tt model to one
generated by MC@NLO and take the full difference as a
systematic uncertainty. We also consider systematic uncertainties associated with the description of initial- and finalstate radiation [36], uncertainties in the efficiency of
reconstructing leptons and identifying b-quark jets, and
uncertainties in the contribution from multiple interactions. In addition, we consider a variation of the Q2 scale
of W-boson þ jet events in ALGPEN. In each case, we treat
the unknown underlying quantity as a nuisance parameter.
Except in the case of the normalization uncertainty, which
affects only the overall rates, for each source of uncertainty
we measure the distortion of the mbb spectrum for positive
and negative fluctuations of the underlying quantity.
Table I lists the contributions of each of these sources of
systematic uncertainty to the yields.
We validate our modeling of the SM backgrounds in four
background-dominated control regions. Each control
region preserves one lepton and at least four jet requirements with additional requirements per region. Events in
the first region are used to study the W þ W bb and W bb
mass reconstruction, requiring at least one b-tagged jet and
bb mass smaller than 100 GeV=c2 . The second region
probes bb and W þ W bb mass reconstruction, requiring
at least one b-tagged jet and W bb mass smaller than
250 GeV=c2 . The third region tests the modeling of
W bb and bb mass reconstruction, requiring at least one
b-tagged jet and W þ W bb mass less than 450 GeV=c2 .
TABLE II. Signal region definitions and expected and observed 95% C.L. upper limits on the production cross section times
branching fraction for each Higgs-boson mass hypothesis. Theoretical predictions are also shown [39–41].
(mH0 , mH ) (GeV=c2 )
325, 225
400, 300
425, 225
500, 300
500, 400
525, 225
600, 300
600, 400
700, 400
700, 600
725, 225
800, 300
800, 600
900, 400
900, 600
1100, 600
mH (GeV=c2 )
mH0 (GeV=c2 )
>175
>225
>200
>200
>350
>100
>200
>350
>325
>450
>425
>275
>475
>450
>475
>475
>275
>325
>375
>450
>450
>500
>550
>550
>650
>650
>700
>750
>725
>775
>800
>975
121801-6
Expected (Observed) Limit (fb)
1100
960
900
470
510
420
200
210
90
10
90
50
43
28
24
13
(1300)
(1100)
(960)
(590)
(700)
(460)
(180)
(250)
(100)
(96)
(120)
(51)
(46)
(36)
(29)
(15)
Theory (fb)
34
18
13
3.9
3.9
2.5
0.76
0.76
0.15
0.15
0.10
3 102
3 102
6 103
6 103
2 104
PRL 110, 121801 (2013)
PHYSICAL REVIEW LETTERS
The fourth region tests the modeling of the W-boson þ jets
background, requiring exactly zero b-tagged jets and
W þ W bb mass greater than 450 GeV=c2 . Assuming an
H 0 -production cross section of 250 fb, each control region
is expected to have negligible signal contamination, with
the exception of the zero b-tag region which would include
signal events at approximately 10% of the sample. For two
of the control regions, Fig. 2 shows the reconstructed bb
mass distributions which, along with other similar distributions, indicate that the background mass distributions are
well modeled within systematic uncertainties.
Figure 3 shows the observed distribution of events in a
representative signal region compared to possible signals
and estimated backgrounds. At each Higgs-boson mass
hypothesis, we fit the most likely value of the Higgsboson cross section by performing a maximum-likelihood
fit in the binned mbb distribution, allowing for systematic
and statistical fluctuations via template morphing [37].
No evidence is found for the presence of Higgs-boson
cascade decays in WWbb events. We set upper limits on
Higgs production at 95% confidence level using the
C.L. method [38], without profiling the systematic uncertainties. The observed limits are consistent with expectation for the background-only hypothesis; see Fig. 4 and
Table II.
In conclusion, we report on the first search for multiple
Higgs bosons in cascade decays. For each accepted event,
we reconstruct the lightest neutral Higgs-boson mass (mbb )
and find the CDF data to be consistent with standard
model background predictions. We calculate 95% C.L.
upper limits on the cross section of such Higgs-boson
production, assuming a 100% branching ratio of H 0 to
W H and H to W h0 , from 1.3 to 0.015 pb for masses
ranging from ðmH0 ¼ 325;mH ¼ 225Þ GeV=c2 to ðmH0 ¼
1100; mH ¼ 600Þ GeV=c2 , respectively, and interpret the
limits in terms of a simplified two-Higgs-doublet model.
While the limits cited here do not exclude any region in the
mH0 mH plane in the simplified model used, they are
the first such limits available. The larger center-of-mass
energy and integrated luminosity of data collected by the
LHC experiments are likely to have the sensitivity to
discover or exclude such models.
We thank the Fermilab staff and the technical staffs of the
participating institutions for their vital contributions. This
work was supported by the U.S. Department of Energy and
National Science Foundation; the Italian Istituto Nazionale
di Fisica Nucleare; the Ministry of Education, Culture,
Sports, Science, and Technology of Japan; the Natural
Sciences and Engineering Research Council of Canada;
the National Science Council of the Republic of China;
the Swiss National Science Foundation; the A. P. Sloan
Foundation; the Bundesministerium für Bildung und
Forschung, Germany; the Korean World Class University
Program and the National Research Foundation of Korea;
the Science and Technology Facilities Council and the
week ending
22 MARCH 2013
Royal Society, U.K.; the Russian Foundation for Basic
Research; the Ministerio de Ciencia e Innovación and
Programa Consolider-Ingenio 2010, Spain; the Slovak
R&D Agency; the Academy of Finland; and the
Australian Research Council (ARC).
121801-7
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Deceased.
Visitor from Istituto Nazionale di Fisica Nucleare, Sezione
di Cagliari, 09042 Monserrato (Cagliari), Italy.
c
Visitor from University of California Irvine, Irvine, CA
92697, USA.
d
Visitor from University of California Santa Barbara, Santa
Barbara, CA 93106, USA.
e
Visitor from University of California Santa Cruz, Santa
Cruz, CA 95064, USA.
f
Visitor from Institute of Physics, Academy of Sciences of
the Czech Republic, 18221 Czech Republic.
g
Visitor from CERN, CH-1211 Geneva, Switzerland.
h
Visitor from Cornell University, Ithaca, NY 14853, USA.
i
Visitor from University of Cyprus, Nicosia CY-1678,
Cyprus.
j
Visitor from Office of Science, U.S. Department of
Energy, Washington, DC 20585, USA.
k
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l
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Prefecture 910-0017, Japan.
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Mexico.
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Visitor from University of Iowa, Iowa City, IA 52242,
USA.
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577-8502, Japan.
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66506, USA.
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